Television receiver



June 20, 1950 P. K. WEIMER Y TELEVISION RECEIVER Fi1ed oct. 12. 1946 ATTO R N EY Patented June 20, 1950;

E ",TELEvIs'IoN RECEIVER ,1'- of Delaware The presentinvention `relates to television, and more particularly totelevision receivingsystems of the projection type which are adapted for the reproduction of images inucolor;

InA United States Patent No'. 2,273,8Q1 granted toD. OQLandiathere is disclosed atelevisionreceiver arrangement in which 'an image' appearing on the luminescent screenof a cathode ray'tube is projected -by means of a spherical mirror through a correcting plat'e onto 'a translucent viewing screen lying inthe `focal plane of the opi tti-calsystem.` `In one embodiment, anadditional mirror, `having a plane surface `and lying at an angle ofsubstantially 45 to the optical axis of thesystem, is `interposedin the optical pathloe#` tween the translucent screen andthe correcting plate, thusvpermitting the screen to'be positioned` forv optimum viewing of theimagereproduced1 thereon.l E j l In" orderto adapt a television receiver of`` they projection .type (ofnwhich vthe' abovementioned Landis system is an illustration) for the reproduce, tion of images invcolor it Vhas beenproposed to` modify the usualconstructionof the` ,cathode ray image-reproducing tube employed therein` This' modifi-cation might consist, for example, infre" placing the standardphosphoresoent screennor-` rnally producing `white light from the tube withY a `screen composed lof phosphors lai'ddown side-f by-,side in the formof narrowl strips and capable; of v"emitting `light in different selected primary `or component colors of'anj additiveI oolor'systemlV whenjthephosphorsare impacted ,by an electrony scanning beam. (For a so-oalled two-,color system, alternate strips, corresponding to` linetrav-` ersals of the cathode ray'beam, ltilouldloe arranged to luminesce in bluish-green and yellowishorange. For a tricolor system,.t he strips wou1d preferably be arrangedadjacentlto one anotherin a predetermined pattern', theseveral strips loe,-l ing of such luminescent compounds asto become luminescent in red, blue or green lightunder elecl tron beam. impact Examples, Qfwmpcuadsef. this type --are setforth,forfinstanca bylieverenz Ina tri-colorisystemQsuchas thefaboveithe, Ireceived television signals comprise three groups;

reproducingy cathode ray tube., If thesestrips of, luminescent *Paul K. Weimer, Princetom J., assignore tol Radio Corporation of America, a corporation 5i-,ligation octor 12, 1945, sensi No. 703,051) f3 'claims (o1. 17a- 5.4)

ing to the integrated values of the selected component or primary blue,` red and green colors of the elementall area of the image being televised will be perceived by an observer. It will be appreciatedthat the colored phosphor strips in such an arrangementmust be very narrow in order to. provide a system having adequate image'resolution anddenition.v For example, in`a tri-color l televisiorisys'temhaving 400-line definition, 1,200y

:olored phosphor strps are required. If the height ofthe luminescent'screen is limited to 4% for a' proj ection-,fty-pe cathode rray tube, then each phos-` phorescent strip will have a width in the order of ,1 millimeter.

An alternativefarrangement to the above consists .in employing an allfwhite phosphor screen, and then mounting color filter strips in proper order on,v or` close to,` the phosphorescent screen i material.' This proximity of the color lter Si) another, and also allows the utilizationeof com-Vv strips to the phosphoris essential in order to accommodate a wide viewing angle, and, hence, the

color filter `strip'smust be located within the tube envelope. HI-liowever, it has been found `that the evacuation processutiliz'ed in the manufacture of cathode ra'yhtubes` renders the use of ordinary color filters impractical, and that specially prepared filter' elements are necessary.

The presentl invention provides meanswhereby l. color filter strips, as employed in a color television j mercially available filters. Moreover, since a feature ofthe present invention resides in the fact that the color filter strips are external to, and

physicallyk separated from, the image-reproducing y tube, 4thev latterv may be of any suitable design having a' conventional uni-colored screen. This is of importance as regards servicing costs when replacement of the cathode ray tubeis necessary.

In'addition, the color lter strip assembly ofthe h l y h e l M V 4 h ,present inventionis located vin that portionY of inUnit'ed `States Patent 2,310,861; granted:A 45

aterialaremade the receiver housing remote from the remainder of thetelevisionl receiving apparatus, and hence is relatively free from thevpossibility ofdamage resulting'from electrical or mechanical failure of some portion of the rreceiving apparatus.

One object ofthe present invention, therefore, is to providean improved televi-sion receiving sysl tem of the projection type Whichis particularly adapted for ythe reproduction of. images in color. fAnother'objectl'of the present invention is to,

sulciently narrow, aresultant'color' correspon'd-"Il` provide a color television receiver of the projection type in which a color filter element assembly is mounted adjacent to, and substantially coplanar with, the translucent viewing screen.

ther objects and advantages will be apparent from the following description of a preferred form of the invention and from the drawing, in which:

Fig. 1 isa .partly sectional View of a projectiontype color television receiver in accordance with the present invention;

Fig. 2 is a detailed view of a portion of Fig. 1,; and

Fig. 3 is a front view of the translucent -screen illustrated in Figs. 1 and `2, with part of the screen broken away to show the location of the color filter strips.

Referring now to the drawing and to Fig. 1 in particular, there is shown `a television receiver of the console type including a cabinet :or hous ing indicated by the reference numeral lil. The cabinet li! is provided in the upper portion thereof with a translucent screen II, composed of material such, for example, as lplastic or ground glass, and upon which the televised image is reproduced orviewing A,by observers.

A lcathode ray tube "I2 ofthe projection type is positioned vin the lower portion of the cabinet II! in such a'mannjer Vthat the `fluorescent screen I3 of the tube faces a 'spherical mirror 14. Tube |2 is supported from a partition or shelf I5 by means including a mounting member I5. A defiecting -yoke I'I, which may 'be of any suitable construction, is provided for the purpose of deilecting 4the electron scanning beam developed within tube I2 in mutually perpendicular directions to trace the image raster in tube I2.

Also supported by the 'partition or shelf I5 is a correcting plate |18, this correctinglens or plate 'I8 lbeing located at orclose to the center of curvature of the spherical vmirror i4, and serving to direct the light 'rays originating at the iiuorescent screen :I3 of tube 'I2 'and reflected from the spherical mirror i4 toward the translucent screen 4II,` all as explained in the mentioned Landis patent. A vplane mirror 'I9 'is mounted inthe upper portion ofthe cabinet 'I'.U, as illustrated, and lies 'at an'angleof approximately 45 tothe 'optica-lexis Yofthe assembly consisting of tube lI2, spherical mirror "r4, and correcting plate I8. Aplural'ity ofscrews '20 are provided rto facilitate positioning and adjustment of the correctingplate I8. v

A -sound :loud-speaker 2I andthe television receiver chassis 22 may 'be located within the receiver cabinet It in the positions villustrated for reproducing the audio 4portions of received signal components.

A filter support 23, preferably comprising va thin sheet of some 'suitable transparent material such as clear glass or plastic (such as methylmethacrylate), lies Lin back of, and substantially coplanar with, the translucent screen I-I. As best shown in Fig. A2, this lter support 23 is mounted in -close vproximity to the inner surface of nthe translucent image viewing screen A plurality of colored filter strips, .generally indicated in the drawing by :the reference numeral 24, are securely aflixed to the rear surface of the filter -support '23, `preferably by means of some suitable adhesive medium. `These filter strips 24 are composed of materials which respectively transmit (for ,a tri-:color'television system) only :the primary colors red, green `and blue, and their mountingvposition iS .Chosen to corf are arranged in an alternate manner, as indicated F-ig. 2 by the letters R, G and B.

The .correcting lens 0r plate I8 is so designed 4as to bring the llight rays originating at the fluorescent Ascreen L3 to a focus on the rear surface of the translucent screen II, as indicated by the 'broken-line light paths in Fig. 1. Since the color lilter strip assembly 24 is located very close to the rear surface of screen I I, however, the scanning light spot is Aalso ,substantially in focus on the .rear surface of the iilter assembly 24.

lThe relative size `of the 'color iilter strips 2'4 has been ,greatly exaggerated jin the Vdrawing in the interest of clarity of illustration. Actually, a single series `or .unit o'f 'the lter strips 24 (or, in other words, a single red strip, a single green strip, and a single blue strip) are of vsuch width that together 'they are .equai 'to 4the diameter of the normal scanning light spot which traverses the screen III during the reconstitution of black and white television images. Accordingly, in the present invention, the diameter of the scanning light spot on screen 1I is reduced 'to one-third of that for correspondingblack ,and white television reception. As a result, a color image is reproduced having a nneness of .detail equal to that of a corresponding black and white image. Of course, the strips 24 may, if desired, each be o'f the diameter of the normal scanning light spot black and white television, .and the scanning spot size maybe the jsame as for 'black and white television. ,Howeven in this case, the color structure of `rthe reproduced image will be more conspicuous.

' disclosureto replace the rstrips '24 with ,an array of colored dots forming various geometric patterns. Insuch `an event, however, it is 4necessary that the arrangement .of Ithe colored dots bear a definite relationship 'to the line-scanning operation of the cathode ray tube fI2.

The operation or" the 'disclosed Asystem may be similar to `that of the known Asystem hereinbefore mentioned in which color 'filter strips are lenclosed within the envelope 'of the cathode ray tube. "Therefore, Athe loperation of the Ypresent invention will not be described in detail, and it is deemed sucientto `mention that, as previously stated, 'the received television signals may comprise three groups, the first group being generated .by 'light Vtrom 'the object 'being telcvised passing throrrgh .a fred filter, the second group 'being generatedby flight 'from the object being televised ,passing'lthrough a .greeniilten .and

,i athird group4 0f .signals being generated by light from the object being televised passing through a blue filter. With proper synchronizationbetween the transmitter and receiver, the electron scanning beam developed within tube i2 wiil cause a spot of light to traverse each one oi the red nlter strips 2d during the period that the group oi signals corresponding to the red color component ci the object being televised is being received, and, in a similar manner, each one of the green and blue lter strips 2d- `during the reception times of the groups oi signals corresponding to the green and blue color components, respectively, o the object being televised. Due to the persistency of vision, an observer will see a resultant color corresponding to the integrated `Values of these color components, and the actual color oi each particular lelemental area of the object being televised will be accurately reproduced on the viewing screen l i.

It is within the scope of the present invention to utilize a type of cathode ray tube i2 having a particular electrode structure, such, for example, as that set forth in my copending United States Patent application Serial No. 5,431 filed January 30, i943, and entitled Television Receiving Systems. It is then necessary that such electrode structure be in registry with the color filter strips 24. This is merely a question of alignment ii there is no geometric distortion in the optical f light path between the tube i2 and the screen l l.

If such geometric distortion exists, however, it may be compensated orby slightly curving the filter strips 2i so `that they will conform to the shadow pattern projected on the screen li by the particular electrode structure of the cathode ray tube.

It is also within the scope of the present invention to employ a system ofr scanning such as set forth in my copending application Serial No. 5,431, abovementioned. In this system, the electron scanning beam moves transverse, or perpendicular to the filter strips .24. For line scaning in a horizontal direction, therefore, the color llter strips 2li are vertically mounted. The video signal which is applied to the control electrode of the image reproducing device I2 is switched from that representative of one color to that representative of another color at a rate in synchronism with the speed at which the electron scanning beam crosses the adjoining color lter strips. In other words, when the 'electron scanning beam is crossing the green color filter strip, for example, the video signal applied to the control electrode of the image reproducing device is representative of the green color component of the object being televised. As the beam crosses the blue strip, the video signal is switched to that representative of blue, etc. The resultant imageappearing on the translucent screen i i is similar to that described above.

Inasmuch as the present disclosure provides for a rigidly-positioned color lter element assembly in television receivers oi the projection type, it,`

is clear that the particular arrangement of the image-projection apparatus forms no specific` the color filter element assembly of` the present` invention through one or more lenses having any suitable focal length. In this case, all or part of the spherical mirror M, correcting plate I8,

and plane mirrorle of Fig. 1 may be omitted, as

well as their associated elements.

It is further within the scope ci the present invention to eliminate the viewing screen il of Figs. l, 2 and 3. The outer surface ol the filter support 2t may then be roughened so that the projected image will be caused to appear thereon. As an alternative, the filter support 2t itself may be made of translucent material. Still iurther, if no support for the color iilter elements 2t is required, the member 2s may be entirely omitted and one surface oi the color iilter elements 2li roughened to act directly as a viewing medium.

Ii desired, various systems of interlaced scanning (such as double or triple interlace) may be employed in connection with the present disl closure without departing from the spirit of the` invention.

I claim:

l. In a television image projection device adapted for the reproduction or ima-ges in color, the combination of a cathode ray tube having a luminescent target area upon which an optical image is produced through the line-by-line scanning action of the electron beam developed within said tube, a spherical reector having" its concave surface area positioned to receive the light of the image as produced on the tube target area,

an aspnerical zone plate located external to the tube-to-rerlector light path, a translucent projection screen positioned in tne iocal plane of said aspherical zone plate,said zone plate-being arranged to receivey light from the renector and to provide a sharply i'ocused enlarged image oi' the f tube target area on the said projection screen,`

and a color iilter assembly including a relatively thin sheet or' transparent material mounted in i closely spaced-apart vco-planar relation with that surface or said projection screen iacing'said aspherlcal zone plate, and a plurality oi' color nlter strips supported and positioned by said transparent sheet, said color iilter strips being arranged in registry with the line-scanning traversals across said projection screen of the image-producing light spot reiiectcd from the lumi- REFERENCES CITED The following references are of record in th file oithis patent:

UNITED STATES PATENTS Number 4 Name Date 2,273,801 Landis Feb. 17. 1942 2,287,307 Herbst June 23, 1942 2,296,908 Crosby Sept. 29, 1942 2,310,863 Leverenz Feb, 9, 1943 2,415,059

Zworylrin Jan. 28, 1947 

